This invention relates to a semiconductor light emitting device which has a light reflecting film formed on the back surface of a substrate transmittable of the light emitted by the light emitting layer so that the light is radiated through the surface of semiconductor layers formed overlying the substrate. More particularly, this invention is concerned with a semiconductor light emitting device which is formed by a chip into which a substrate wafer is sliced (wherein groove lines are formed by using a diamond cutter) with the wafer easily positioned in position.
There is a known method of enhancing the light radiation efficiency for semiconductor light emitting devices that are adapted to radiate light transmitted through a substrate thereof, wherein a light reflecting film is formed on the back surface of the substrate so that the portion of the light emitted toward the back surface of the substrate can be effectively reflected by the light reflecting film, thereby improving light radiation efficiency. For example, the light emitting device for bluish light radiation (e.g. from ultraviolet ray to yellow portion) has gallium-nitride based semiconductor layers epitaxially grown on a sapphire (Al.sub.2 O.sub.3 single crystal) substrate transmittable of bluish light therethrough.
The semiconductor light emitting device having such gallium-nitride based semiconductor, layers for bluish light radiation is basically structured as shown in FIG. 4. That is, the semiconductor light emitting device includes a sapphire substrate 21. The sapphire substrate 21 has thereon a low-temperature buffer layer 22, e.g. of GaN, an n-type layer (cladding layer) 23 of n-type GaN epitaxially grown at a high temperature on the buffer layer 22, an active layer (light emitting layer) 24, e.g. of InGaN-based compound semiconductor having a bandgap energy lower than that of the cladding layer to define an emission light wavelength, and a p-type layer (cladding layer) of p-type GaN. Incidentally, the "InGaN-based" means a chemical composition having In and Ga variable in content ratio. The semiconductor layers has a p-side electrode 28 on a surface thereof and an n-side electrode 29 on a surface of the n-type layer 23 exposed by partly etching the overlying semiconductor layers. With such structure, a light reflecting film 21a is formed for example by an Al thin film over the entire back surface of the substrate 21 in order to reflect toward the p-side electrode 28 and hence effectively utilize the light travelling toward the substrate.
In the meanwhile, the semiconductor light emitting device of this kind is constituted by a chip having a size, for example, of 360 .mu.m by 360 .mu.m. That is, a multiplicity of chips are manufactured through wafer processing using a circular wafer having a diameter of approximately 2 inches so that the wafer being processed is finally divided into individual chips thereby providing light emitting devices. The wafer division is generally through dicing processes. However, where the wafer is, for example, too hard and hence difficult to carry out dicing thereon, e.g. as in the case of a sapphire wafer formed thereon with gallium-nitride based semiconductor layers for light emission, the wafer is subjected at its back surface to slicing using a diamond pen so as to be broken into individual chips.
However, if the light reflect film is formed covering over the entire back surface of the wafer, the semiconductor layer chip pattern existing on the main surface of the wafer is impossible to recognize as viewed the back surface side of the wafer during slicing the back surface to divide the wafer in a manner stated above. This result in difficulty in positioning for slicing operations on the wafer.